Despite ongoing efforts to define immunologically relevant tumor antigens, very little is known about most tumor rejection antigens for the majority of human cancers. Consequently, most cancer vaccine approaches currently use tumor cells as a source of antigen. Early generations of cell-based cancer vaccines have consisted of killed tumor cells or tumor cell lysates mixed with adjuvants, such as Bacillus Calmette Guerin (BCG) and Corynebacterium parvum, in an attempt to amplify tumor-specific immune responses (Berd et al., J. Clin. Oncol. 8: 1858-1867 (1990)). Subsequently, genetically modified tumor vaccines replaced the most complex and inconsistent mixtures of tumor cells and bacteria. Currently, the most popular genetically modified cell-based vaccines take advantage of the large set of cloned genes encoding cytokines and co-stimulatory molecules (Pardoll, Ann. Rev. Immunol. 13: 399-415 (1995)).
Among the different cytokines used to modify tumor immunogenicity, granulocyte-macrophage colony stimulating factor (GM-CSF) appears to be the most potent (Dranoff et al., PNAS USA 90: 3539-3543 (1993)). GM-CSF induces the differentiation of primitive hematopoietic precursors into dendritic cells (DC), a type of antigen-presenting cell (APC) that initiates the most potent T-cell responses (Banchereau et al., Nature 392 (6673): 245-252 (1998)) and promotes DC recruitment and differentiation at the site of vaccination. Thus, DC play a central role in priming immunological response.
GM-CSF-secreting cellular vaccines have been shown to eradicate small, pre-established tumors in mice (Dranoff et al., supra; and Levitsky et al., J. Immunol. 156: 3858-3865 (1996)). Furthermore, promising results have been obtained in human patients afflicted with melanoma (Soiffer et al., PNAS USA 95: 13141-13146 (1998)), prostate and renal cell carcinoma (Simons et al., Cancer Res. 59: 5160-5168 (1999); and Simons et al., Cancer Res. 57: 1537-1546 (1997)), and pancreatic cancer (Jaffee et al., J. Clin. Oncol. 19: 145-156 (2001)). These trials consistently demonstrated systemic anti-tumor immunity in patients and suggest an improvement in overall survival in those patients in whom evidence of vaccine efficacy was demonstrated by the development of tumor-specific delayed type hypersensitivity (DTH) responses (Jaffee et al., supra).
Unfortunately, modification of autologous tumor cells to express a cytokine, such as GM-CSF, is highly individualized, expensive, and labor-intensive. Therefore, simpler approaches that maintain the immunological activity of paracrine cytokine production have been developed. One such approach utilizes a universal bystander cell line altered to produce a large and stable amount of GM-CSF (see, e.g., Levitsky et al., U.S. Pat. No. 6,464,973 and Int'l Pat. App. No. PCT/US99/02253) in combination with an antigen of the cancer to be treated, such as, for example, tumor cells isolated from the patient (Borrello et al., Hum. Gene Ther. 10: 1983-1991 (1999); Borrello et al., Blood 95: 3011-3019 (2000)). This approach obviates the need for in vitro passaging or modification, such as by transduction, of each patient's tumor cells, thereby guaranteeing a constant amount of cytokine production without any intra- or inter-patient variability, while utilizing the patient-specific antigenic repertoire. An allogeneic, GM-CSF-secreting human erythroleukemia cell line, namely K562, is currently being used in two phase I trials at Johns Hopkins University for vaccination of multiple myeloma and acute myelogenous leukemia (AML), in combination with irradiated autologous tumor cells.
Vaccination of mice afflicted with lymphoma with a mixture of autologous tumor cells and GM-CSF-producing MHC class I- and MHC class II-negative cells, namely B78H1/GM-CSF cells, primed an anti-tumor immune response. The anti-tumor immune response was equivalent to or better than those achieved using autologous tumor cells directly transduced to secrete GM-CSF.
GM-CSF-secreting cellular vaccines, which are currently in use, are not specific for a defined tumor antigen. Hence, it is not possible to target such vaccines and evaluate fully their anti-tumor immune responses. It is an object of the present invention, therefore, to provide a GM-CSF-secreting cellular vaccine that is specific for a defined tumor antigen. Such a vaccine will enable one to evaluate more fully anti-tumor immune responses. This and other objects and advantages of the present invention, as well as additional inventive features, will become apparent from the detailed description provided herein.